U.S. patent application number 12/821961 was filed with the patent office on 2011-06-09 for polymer blend proton exchange membrane and method for manufacturing the same.
This patent application is currently assigned to BEIJING PRUDENT CENTURY TECHNOLOGY CO., LTD.. Invention is credited to Mianyan HUANG, Linlin LI, Yanling ZHAO.
Application Number | 20110136016 12/821961 |
Document ID | / |
Family ID | 44082356 |
Filed Date | 2011-06-09 |
United States Patent
Application |
20110136016 |
Kind Code |
A1 |
HUANG; Mianyan ; et
al. |
June 9, 2011 |
POLYMER BLEND PROTON EXCHANGE MEMBRANE AND METHOD FOR MANUFACTURING
THE SAME
Abstract
The present invention relates to a polymer blend proton exchange
membrane comprising a soluble polymer and a sulfonated polymer,
wherein the soluble polymer is at least one polymer selected from
the group consisting of polysulfone, polyethersulfone and
polyvinylidene fluoride, the sulfonated polymer is at least one
polymer selected from the group consisting of sulfonated
poly(ether-ether-ketone), sulfonated
poly(ether-ketone-ether-ketone-ketone), sulfonated
poly(phthalazinone ether keton), sulfonated phenolphthalein
poly(ether sulfone), sulfonated polyimides, sulfonated
polyphosphazene and sulfonated polybenzimidazole, and wherein the
degree of sulfonation of the sulfonated polymer is in the range of
96% to 118%. The present invention further relates to a method for
manufacturing the polymer blend proton exchange membrane.
Inventors: |
HUANG; Mianyan; (Beijing,
CN) ; ZHAO; Yanling; (Beijing, CN) ; LI;
Linlin; (Beijing, CN) |
Assignee: |
BEIJING PRUDENT CENTURY TECHNOLOGY
CO., LTD.
Beijing
CN
|
Family ID: |
44082356 |
Appl. No.: |
12/821961 |
Filed: |
June 23, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
PCT/CN2009/001372 |
Dec 4, 2009 |
|
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12821961 |
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Current U.S.
Class: |
429/309 ;
264/331.19; 429/314 |
Current CPC
Class: |
H01M 8/1081 20130101;
H01M 8/1032 20130101; H01M 8/1023 20130101; H01M 8/1044 20130101;
C08G 65/48 20130101; Y02E 60/50 20130101; H01M 8/103 20130101; Y02E
60/523 20130101; C08G 2261/722 20130101; H01M 8/1027 20130101; C08L
71/00 20130101; C08L 81/06 20130101; H01M 8/20 20130101; H01M
8/1011 20130101; H01M 8/188 20130101; C08J 2381/06 20130101; Y02P
70/56 20151101; Y02P 70/50 20151101; C08J 5/2275 20130101; H01M
8/1025 20130101; C08L 71/00 20130101; C08L 71/00 20130101; C08L
81/06 20130101; C08L 81/06 20130101 |
Class at
Publication: |
429/309 ;
264/331.19; 429/314 |
International
Class: |
H01M 10/0565 20100101
H01M010/0565; C08J 5/22 20060101 C08J005/22; H01M 8/10 20060101
H01M008/10 |
Claims
1. A polymer blend proton exchange membrane comprising a soluble
polymer and a sulfonated polymer, wherein the soluble polymer is at
least one polymer selected from the group consisting of
polysulfone, polyethersulfone and polyvinylidene fluoride, the
sulfonated polymer is at least one polymer selected from the group
consisting of sulfonated poly(ether-ether-ketone), sulfonated
poly(ether-ketone-ether-ketone-ketone), sulfonated
poly(phthalazinone ether keton), sulfonated phenolphthalein
poly(ether sulfone), sulfonated polyimide, sulfonated
polyphosphazene and sulfonated polybenzimidazole, and wherein the
degree of sulfonation of the sulfonated polymer is in the range of
96% to 118%.
2. The polymer blend proton exchange membrane according to claim 1,
wherein the degree of sulfonation is 98 to 116%, preferably 100 to
114%, more preferably 106 to 110%.
3. The polymer blend proton exchange membrane according to claim 1,
wherein the sulfonated polymer is made from an unsulfonated polymer
with melt viscosity of 100 to 550 centipoise, preferably 300 to 450
centipoise, more preferably 350 to 400 centipoise, at 300 to
500.degree. C.
4. The polymer blend proton exchange membrane according to claim 1,
wherein the sulfonated polymer is prepared by directly dissolving
the unsulfonated polymer in concentrated sulfuric acid, Nordhausen
acid, or chlorosulfonic acid and sulfonating the unsulfonated
polymer.
5. The polymer blend proton exchange membrane according to claim 1,
wherein the sulfonated polymer is prepared by directly dissolving
the unsulfonated polymer in concentrated sulfuric acid and
sulfonating the unsulfonated polymer, the concentrated sulfuric
acid is used in an amount of 2 to 15 ml of concentrated sulfuric
acid per gram of unsulfonated polymer, preferably 5 to 7 ml of
concentrated sulfuric acid per gram of unsulfonated polymer.
6. The polymer blend proton exchange membrane according to claim 4,
wherein the sulfonated polymer is prepared by two steps: the first
step is to carry out reaction for 3 to 5 hours at 20 to 40.degree.
C.; the second step is to carry out reaction for 1 to 4 hours at 70
to 100.degree. C.
7. The polymer blend proton exchange membrane according to claim 6,
wherein the resulting sulfonated polymer is shaped through
water-cooling, preferably through a process in which the resulting
sulfonated polymer slurry is poured into a screen with 1 to 4 mm
mesh size and flows into deionized water beneath the screen and a
strip-shaped sulfonated polymer is obtained after stirring.
8. The polymer blend proton exchange membrane according to claim 7,
wherein the resulting strip-shaped sulfonated polymer is washed to
remove remaining sulfuric acid, then is dried at a temperature of
100 to 120.degree. C. for at least 1 hour, preferably at least 4
hours.
9. The polymer blend proton exchange membrane according to claim 1,
wherein the weight-average molecular weight of the soluble polymer
is in the range of 35000 to 65000, preferably 45000 to 55000, more
preferably 48000 to 52000.
10. The polymer blend proton exchange membrane according to claim
1, wherein the content of the soluble polymer is 10% to 50%,
preferably 13% to 38%, more preferably 18% to 35%, most preferably
22% to 32%, based on the total weight of the membrane.
11. The polymer blend proton exchange membrane according to claim
1, wherein the thickness of the polymer blend proton exchange
membrane is in the range of 30 to 200 .mu.m, more preferably 50 to
100 .mu.m.
12. A method for manufacturing a polymer proton exchange membrane
comprising the following steps: a) dissolving a soluble polymer in
an organic solvent and obtaining a uniform solution, wherein the
soluble polymer is at least one polymer selected from the group
consisting of polysulfone, polyethersulfone and polyvinylidene
fluoride; b) dissolving a sulfonated polymer in the solution
obtained in step a) and obtaining a membrane forming solution,
wherein the sulfonated polymer is at least one polymer selected
from the group consisting of sulfonated poly(ether-ether-ketone),
sulfonated poly(ether-ketone-ether-ketone-ketone), sulfonated
poly(phthalazinone ether keton), sulfonated phenolphthalein
poly(ether sulfone), sulfonated polyimide, sulfonated
polyphosphazene and sulfonated polybenzimidazole, and wherein the
degree of sulfonation of the sulfonated polymer is in the range of
96% to 118%; c) forming a membrane by tape casting the membrane
forming solution, then removing the membrane after being dried and
heat-treated.
13. The method according to claim 12, wherein the method further
includes a step: d) immersing the membrane in sulfuric acid aqueous
solution for a whole day and taking out the membrane for later
use.
14. The method according to claim 12, wherein the degree of
sulfonation of the sulfonated polymer is 98 to 116%, preferably 100
to 114%, more preferably 106 to 110%.
15. The method according to claim 12, wherein the sulfonated
polymer is made from an unsulfonated polymer with melt viscosity of
100 to 550 centipoise, preferably 300 to 450 centipoise, more
preferably 350 to 400 centipoise, at 300 to 500.degree. C.
16. The method according to claim 12, wherein the sulfonated
polymer is prepared by directly dissolving the unsulfonated polymer
in concentrated sulfuric acid, Nordhausen acid, or chlorosulfonic
acid and sulfonating the unsulfonated polymer.
17. The method according to claim 12, wherein the sulfonated
polymer is prepared by directly dissolving the unsulfonated polymer
in concentrated sulfuric acid and sulfonating the unsulfonated
polymer, and wherein the concentrated sulfuric acid is used in an
amount of 2 to 15 ml of concentrated sulfuric acid per gram of
unsulfonated polymer, preferably 5 to 7 ml of concentrated sulfuric
acid per gram of unsulfonated polymer.
18. The method according to claim 16, wherein the sulfonated
polymer is prepared by two steps: the first step is to carry out
reaction for 3 to 5 hours at 20 to 40.degree. C.; the second step
is to carry out reaction for 1 to 4 hours at 70 to 100.degree.
C.
19. The method according to claim 18, wherein the resulting
sulfonated polymer is shaped through a water-cooling process,
preferably through a process in which the resulting sulfonated
polymer slurry is poured into a screen with 1 to 4 mm mesh size and
flows into deionized water beneath the screen and a strip-like
sulfonated polymer is obtained after stirring.
20. The method according to claim 19, wherein the resulting
strip-shaped sulfonated polymer is washed to remove remaining
sulfuric acid, then is dried at a temperature of 100 to 120.degree.
C. for at least 1 hour, preferably at least 4 hours.
21. The method according to claim 12, wherein the weight-average
molecular weight of the soluble polymer is in the range of 35000 to
65000, preferably 45000 to 55000, more preferably 48000 to
52000.
22. The method according to claim 12, wherein the content of the
soluble polymer is 10% to 50%, preferably 13% to 38%, more
preferably 18% to 35%, most preferably 22% to 32%, based on the
total weight of the membrane.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation of International Patent
Application No. PCT/CN2009/001372, filed Dec. 4, 2009, which is
incorporated herein by reference.
TECHNICAL FIELD
[0002] The present invention relates to a polymer blend proton
exchange membrane and the method for manufacturing the same. In
particular, the present invention relates to a polymer blend proton
exchange membrane comprising a soluble polymer and a sulfonated
polymer with proton exchange function. The polymer blend proton
exchange membrane according to the present invention can be used in
redox flow battery, particularly in vanadium redox flow
battery.
BACKGROUND OF THE INVENTION
[0003] Energy crisis and environment pollution are two big problems
for achieving sustainable development of global economics. An
efficient way to solve the two problems is to develop more
effective renewable energy such as wind energy, solar energy, tidal
energy, etc. To ensure stable supply of renewable energy such as
wind energy, solar energy, etc., an energy storage technology with
high capacity, low cost, high efficiency, and high reliability and
without pollution must be developed. Therefore, one of hot spots in
the world in energy field is to develop an energy storage system
with high capacity.
[0004] Among various energy storage systems with high capacity,
vanadium redox battery (VRB) has been put into demonstrative
operation in wind power generation, solar power generation, and the
peak regulation of power grid and the like in foreign countries
because of its unique advantages such as long lifetime, high
reliability, low cost for operation and maintenance, and the
like.
[0005] Vanadium battery uses solutions of vanadium ions with
different valences as active species, wherein V.sup.4+/V.sup.5+
redox couple is used for positive electrode and V.sup.2+/V.sup.3+
redox couple is used for negative electrode. During a charge
process, V.sup.4+ is changed into V.sup.5+ at positive electrode
and V.sup.3+ is changed into V.sup.2+ at negative electrode. During
a discharge process, V.sup.5+ is changed into V.sup.4+ at positive
electrode and V.sup.2+ is changed into V.sup.3+. A cell of vanadium
battery is comprised of a bipolar plate, electrodes and a separator
membrane, wherein the separator membrane of vanadium battery must
be able to prevent vanadium ions of different valences in the
electrolytes for the positive electrode and for the negative
electrode from permeating through the separator membrane but
permitting the transfer of proton of hydrogen through the separator
membrane. Therefore, the separator membrane should have a desirable
proton conductivity as well as a high selective permeability for
protons. Furthermore, the separator membrane must have a long-term
chemical stability and good mechanical properties so as to meet the
long life-time requirement of vanadium battery.
[0006] Currently, the common used membrane in vanadium battery is
the perfluorosulfonic acid proton exchange membrane provided by
DuPont Company under the trade name of Nafion. Perfluorosulfonic
acid proton exchange membrane has excellent chemical stability and
electric conductivity and can meet the requirement of vanadium
battery. However, Perfluorosulfonic acid proton exchange membrane
has poor permselectivity and vanadium ions can permeate through the
membrane during the operation of vanadium battery. Thus, the
self-discharge of vanadium battery occurs and the capacity of
vanadium battery is reduced. Furthermore, the high cost of
perfluorosulfonic acid proton exchange membrane is one of the
factors obstructing the large scale commercialization of vanadium
battery. Therefore, an important step for the commercialization of
vanadium battery is to develop a proton exchange membranes suitable
for use in vanadium battery with low cost, high chemical stability,
good electric conductivity, high permselectivity and high
mechanical strength.
[0007] In the field of fuel battery, in order to reduce the cost of
proton exchange membrane, some non-fluorous hydrocarbon polymers
are extensively studied to be used as the membrane forming material
after being sulforated. Such kinds of polymers generally have
properties such as high chemical and thermal stability, and low
cost, for example, polyethersulfone, poly(ether ketone), polyimide,
polyphosphazene, polybenzimidazole, etc. Theses polymers are
sulforated to form proton exchange membranes, and the resulting
membranes have a property that the properties thereof such as
proton conductivity of the membrane depend on a degree of
sulforation of the polymer. The degree of sulforation of the
polymer shall be high enough so that an ideal conductivity is
obtained. However, when the degree of sulforation of the polymer is
high, a mechanical property and dimensional and chemical
stabilities of the membrane will become poor and thus the
requirement of usage will not be satisfied. The proton exchange
membrane used in the vanadium battery can also be made from these
sulforated polymers. However, these membranes will face a similar
problem, i.e., how to compromise among degree of sulforation,
electric conductivity and chemical stability, mechanical strength,
and vanadium ion permeability.
SUMMARY OF THE INVENTION
[0008] The applicant of the present invention has surprisingly
found that a proton exchange membrane with excellent comprehensive
properties can be manufactured by blending a polymer with high
degree of sulfonation and a soluble polymer.
[0009] Therefore, one object of the present invention is to provide
a polymer proton exchange membrane comprising a soluble polymer and
a sulfonated polymer, wherein the soluble polymer is at least one
polymer selected from the group consisting of polysulfone (PS),
polyethersulfone (PES) and polyvinylidene fluoride (PVDF), the
sulfonated polymer is at least one polymer selected from the group
consisting of sulfonated poly(ether-ether-ketone) (SPEEK),
sulfonated poly(ether-ketone-ether-ketone-ketone) (SPEKEKK),
sulfonated poly(phthalazinone ether keton) (SPPEK), sulfonated
phenolphthalein poly(ether sulfone), sulfonated polyimides (SPI),
sulfonated polyphosphazene and sulfonated polybenzimidazole (PBI),
and wherein the degree of sulfonation of the sulfonated polymer is
in the range of 96% to 118%.
[0010] In the context of this disclosure, the term "soluble
polymer" means that the polymer is soluble in organic solvent. The
organic solvent includes, but not limits to, one or more of
dimethylacetamide, dimethylfomamide, dimethyl sulfoxide, triethyl
phosphate, cyclopentanone, N-methyl-2-pyrrolidone, tetramethylurea,
and propylene carbonate. Preferably, the organic solvent is
selected from one or more of N,N-dimethylfomamide,
N,N-dimethylacetamide, and N-methyl-2-pyrrolidone.
[0011] In a preferred embodiment of the present invention, the
degree of sulfonation of the sulfonated polymer is in the range of
98% to 116%, preferably 100% to 114%, more preferably 106% to
110%.
[0012] In another preferred embodiment of the present invention,
the sulfonated polymer is made from the unsulfonated polymer which
has a melt viscosity in the range of 100 to 550 centipoise,
preferably 300 to 450 centipoise, more preferably 350 to 400
centipoise, at 300.degree. C. to 500.degree. C.
[0013] Preferably, the sulfonated polymer is obtained by directly
dissolving the unsulfonated polymer in concentrated sulfuric acid,
Nordhausen acid, or chlorosulfonic acid and sulfonating the
unsulfonated polymer.
[0014] Preferably, the sulfonated polymer is prepared by directly
dissolving the unsulfonated polymer in concentrated sulfuric acid
and sulfonating the unsulfonated polymer. The concentrated sulfuric
acid is used in an amount of 2 to 15 ml of concentrated sulfuric
acid per gram of unsulfonated polymer, preferably 5 to 7 ml of
concentrated sulfuric acid per gram of unsulfonated polymer.
[0015] Preferably, the sulfonated polymer is prepared by two steps:
the first step is to carry out the reaction for 3 to 5 hours at 20
to 40.degree. C.; the second step is to carry out the reaction for
1 to 4 hours at 70 to 100.degree. C.
[0016] Preferably, the resulting sulfonated polymer is shaped
through a water-cooling process, preferably through the following
process: the resulting sulfonated polymer slurry is poured into a
screen with 1 to 4 mm mesh size and the slurry flows into deionized
water beneath the screen and the strip-like sulfonated polymer is
obtained after stirring.
[0017] Preferably, the resulting strip-like sulfonated polymer is
washed to remove remaining sulfuric acid, then is dried at a
temperature of 100 to 120.degree. C. for at least 1 hour,
preferably at least 4 hours, so as to remove the water
sufficiently.
[0018] In a further preferred embodiment of the present invention,
the weight-average molecular weight of the soluble polymer is in
the range of 35000 to 65000, preferably 45000 to 55000, more
preferably 48000 to 52000.
[0019] In a still further preferred embodiment of the present
invention, the content of the soluble polymer is 10% to 50%,
preferably 13% to 38%, more preferably 18% to 35%, most preferably
22% to 32%, based on the total weight of the membrane.
[0020] The thickness of the polymer blend proton exchange membrane
according to the present invention has no specific limitation, but
can be determined based on the operating requirements, preferably
is in the range of 30 to 200 .mu.m, more preferably 50 to 100
.mu.m.
[0021] Another object of the present invention is to provide a
method for manufacturing a polymer proton exchange membrane,
comprising the following steps: [0022] a) dissolving a soluble
polymer in an organic solvent and obtaining a uniform solution,
wherein the soluble polymer is at least one polymer selected from
the group consisting of polysulfone (PS), polyethersulfone (PES)
and polyvinylidene fluoride (PVDF); [0023] b) dissolving a
sulfonated polymer in the solution obtained in step a) and
obtaining a membrane forming solution, wherein the sulfonated
polymer is at least one polymer selected from the group consisting
of sulfonated poly(ether-ether-ketone), sulfonated
poly(ether-ketone-ether-ketone-ketone), sulfonated
poly(phthalazinone ether keton), sulfonated phenolphthalein
poly(ether sulfone), sulfonated polyimides, sulfonated
polyphosphazene and sulfonated polybenzimidazole, and wherein the
degree of sulfonation of the sulfonated polymer is in the range of
96% to 118%; [0024] c) forming a membrane by tape casting the
membrane forming solution, drying and heat-treating the membrane,
then peeling off the membrane.
[0025] Preferably, the method according to the present invention
can include a further step: d) immersing the membrane in sulfuric
acid aqueous solution for a whole day to make the membrane fully
protonated. Still preferably, the concentration of the sulfuric
acid aqueous solution used in the step d) of the method according
to the present invention is in the range of 0.5 to 1.5 M and the
immersion time is in the range of 15 to 30 hours.
[0026] In a preferred embodiment according to the present
invention, the organic solvent includes, but not limits to, one or
more of dimethylacetamide, dimethylfomamide, dimethyl sulfoxide,
triethyl phosphate, cyclopentanone, N-methyl-2-pyrrolidone,
tetramethylurea, and propylene carbonate. Preferably, the organic
solvent is selected from one or more of N,N-dimethylfomamide,
N,N-dimethylacetamide, and N-methyl-2-pyrrolidone.
[0027] In a preferred embodiment according to the present
invention, the degree of sulfonation (DS) of the sulfonated polymer
is in the range of 98% to 116%, preferably 100% to 114%, more
preferably 106% to 110%.
[0028] In another preferred embodiment according to the present
invention, the sulfonated polymer is made from an unsulfonated
polymer which has a melt viscosity in the range of 100 to 550
centipoise, preferably 300 to 450 centipoise, more preferably 350
to 400 centipoise, at 300.degree. C. to 500.degree. C.
[0029] Preferably, the sulfonated polymer is prepared by directly
dissolving the unsulfonated polymer in concentrated sulfuric acid,
Nordhausen acid, or chlorosulfonic acid and sulfonating the
unsulfonated polymer.
[0030] Preferably, the sulfonated polymer is prepared by directly
dissolving the unsulfonated polymer in concentrated sulfuric acid
and sulfonating the unsulfonated polymer. The concentrated sulfuric
acid is used in an amount of 2 to 15 ml of concentrated sulfuric
acid per gram of unsulfonated polymer, preferably in an amount of 5
to 7 ml of concentrated sulfuric acid per gram of unsulfonated
polymer.
[0031] Preferably, the sulfonated polymer is prepared by two steps:
the first step is to carry out the reaction for 3 to 5 hours at 20
to 40.degree. C.; the second step is to carry out the reaction for
1 to 4 hours at 70 to 100.degree. C.
[0032] Preferably, the resulting sulfonated polymer is shaped
through a water-cooling process, preferably through the following
process. The resulting sulfonated polymer slurry is poured into a
screen with 1 to 4 mm mesh size and the slurry flows into deionized
water beneath the screen, obtaining a strip-like sulfonated polymer
after stirring.
[0033] Preferably, the resulting strip-like sulfonated polymer is
washed to remove the remaining sulfuric acid, then is dried at a
temperature of 100 to 120.degree. C. for at least 1 hour,
preferably at least 4 hours, so as to remove the water
thoroughly.
[0034] In a further preferred embodiment according to the present
invention, the weight-average molecular weight of the soluble
polymer is in the range of 35000 to 65000, preferably 45000 to
55000, more preferably 48000 to 52000.
[0035] In a still further preferred embodiment according to the
present invention, the content of the soluble polymer is 10% to
50%, preferably 13% to 38%, more preferably 18% to 35%, most
preferably 22% to 32%, based on the total weight of the
membrane.
[0036] The thickness of the polymer blend proton exchange membrane
according to the present invention has no specific limitation, but
can be determined based on the operating requirements, preferably
is in the range of 30 to 200 .mu.m, more preferably 50 to 100
.mu.m.
[0037] The proton exchange membrane according to the present
invention can be prepared by well known membrane forming processes
such as tape casting, casting, and the like without any specific
requirement.
[0038] In addition to the use in redox flow battery, in particular
in vanadium redox flow battery, the proton exchange membrane
according to the present invention can also be used in proton
exchange membrane fuel battery, in particular direct methanol fuel
cell.
Preparation and Selection of Sulfonated Polymer
[0039] According to the present invention, a proton exchange
membrane with excellent comprehensive properties is manufactured by
blending a polymer with high degree of sulfonation and a soluble
polymer. The sulfonated polymer with high degree of sulfonation has
excellent proton conductivity, but has poor mechanical properties
and poor dimensional stability. Without bound to any specific
theory, cross-linking between the sulfonated polymer according to
the present invention and the blended soluble polymer can occur,
and such cross-linking will obstruct swelling of the sulfonated
polymer so that the mechanical properties and dimensional stability
are improved and the vanadium ion permeability through the proton
exchange membrane is lowered. Preferably, the degree of sulfonation
(DS) of the sulfonated polymer according to the present invention
is in the range of 96% to 118%, preferably 98% to 116%, more
preferably 100% to 114%, still more preferably 106% to 110%, so as
to ensure the electric conductivity of the sulfonated polymer.
Herein, the degree of sulfonation means the number of sulfonic acid
groups contained in 100 repeating unit.
[0040] The sulfonated polymer used in the proton exchange membrane
according to the present invention can be same kind of sulfonated
polymers with a variety of degrees of sulfonation.
[0041] The sulfonated polymer with high DS used in the proton
exchange membrane according to the present invention is made from
an unsulfonated polymer which has a melt viscosity in the range of
100 to 550 centipoise, preferably 300 to 450 centipoise, more
preferably 350 to 400 centipoise, at 300.degree. C. to 500.degree.
C.
[0042] Preferably, the sulfonated polymer is prepared by directly
dissolving the unsulfonated polymer in concentrated sulfuric acid,
Nordhausen acid, or chlorosulfonic acid and sulfonating the
unsulfonated polymer.
[0043] Preferably, the sulfonated polymer is prepared by directly
dissolving the unsulfonated polymer in concentrated sulfuric acid
and sulfonating the unsulfonated polymer. The concentrated sulfuric
acid is used in an amount of 2 to 15 ml of concentrated sulfuric
acid per gram of unsulfonated polymer, preferably in an amount of 5
to 7 ml of concentrated sulfuric acid per gram of unsulfonated
polymer.
[0044] Preferably, the sulfonated polymer is prepared through two
steps: the first step is to carry out the reaction for 3 to 5 hours
at 20 to 40.degree. C.; the second step is to carry out the
reaction for 1 to 4 hours at 70 to 100.degree. C.
[0045] Preferably, the resulting sulfonated polymer is shaped
through a water-cooling process, preferably through the following
process. The resulting slurry after sulfonation reaction is poured
into a screen with 1 to 4 mm mesh size and the slurry flows through
the screen mesh into deionized water beneath the screen, obtaining
a strip-like sulfonated polymer after stirring.
[0046] Preferably, the resulting strip-like sulfonated polymer is
washed to remove the remaining sulfuric acid, then is dried at a
temperature of 100 to 120.degree. C. for at least 1 hour,
preferably at least 4 hours, so as to remove the water
sufficiently.
[0047] The degree of sulfonation can be controlled by selecting the
amount of sulfuric acid used per unit mass of polymer, sulfonation
temperature, and/or sulfonation time during sulfonation process.
The degree of sulfonation can be determined by acid-base titration
method.
[0048] The sulfonated polymer used in the present invention can be
prepared by utilizing any other technology well known in the
art.
Preparation of Blend Proton Exchange Membrane
[0049] According to the method of the present invention, a polymer
blend proton exchange membrane can be prepared by the following
steps.
[0050] A soluble polymer is dissolved in a certain amount of
solvent with heating and stirring to obtain a uniform solution. A
sulfonated polymer is dissolved in said solution with heating and
stirring to obtain a uniform membrane forming solution. The
membrane forming solution is poured onto a glass plate to conduct
slip casting. The membrane obtained after slip casting is put into
a drying oven and dried at 50 to 90.degree. C. for 8 to 16 hours,
then heat-treated at 80 to 120.degree. C. for 2 to 6 hours. After
cooling, the dried membrane together with the glass plate is
immersed into deionized water and the membrane is removed from the
glass plate. Then, the membrane is immersed in 0.5 to 1.5 M
H.sub.2SO.sub.4 aqueous solution for 20 to 30 hours, then taken out
from the H.sub.2SO.sub.4 aqueous solution, and washed with
deionized water several times to remove remaining H.sub.2SO.sub.4
in the membrane before immersed into deionized water. The thickness
of the proton exchange membrane is determined by controlling the
thickness of tape casted membrane forming solution.
[0051] The polymer blend proton exchange membrane according to the
present invention can be prepared by any other procedure similar to
the process of the present invention without departing from the
scope of the present invention.
[0052] The polymer blend proton exchange membrane according to the
present invention is suitable for use in redox flow battery, in
particular vanadium redox flow battery. The polymer blend proton
exchange membrane according to the present invention has excellent
proton conductivity and low vanadium ions permeability, as well as
good mechanical properties, dimensional stability and chemical
stability, and low cost.
[0053] The polymer blend proton exchange membrane according to the
present invention has at least one of the following advantages.
[0054] 1. The membrane is low cost and easy to obtain. Besides, the
raw materials used in the present invention are commercial
products, and the sulfonation process is easy to operate. [0055] 2.
The membrane has excellent chemical and thermal stability, and high
mechanical strength. Most of the polymer raw materials used in the
present invention are engineering thermoplastics which have good
chemical and thermal stability. The membrane has good electric
conductivity because the sulfonated polymer with high degree of
sulfonation is used. [0056] 3. The blended polymer selected in the
present invention has the advantages such as low cost, good
chemical stability, good membrane forming property. [0057] 4. The
mechanical property and the dimensional stability of the membrane
have been greatly improved since the swell of the blend membrane is
effectively limited by the cross-linking between polymers. [0058]
5. Because of the ion passages of sulfonated polymer itself which
is smaller than those of perfluorosulfonic acid membrane, as well
as the cross-linking effect of the blended polymer, the capability
of the blend membrane to obstruct vanadium ions from permeating the
blend membrane is better than that of perfluorosulfonic acid
membrane. [0059] 6. Compared with perfluorosulfonic acid membrane,
the blend membrane prepared by the method according to the present
invention has a much lower cost, which will definitely promote the
commercialization of vanadium redox flow battery.
DETAILED DESCRIPTION OF THE INVENTION
The Preparation Examples of Sulfonated Polymer
[0060] 1. The Preparation of Sulfonated poly(ether-ketone)
[0061] 10 g of poly(ether-ketone) (Victrex PLC, 22 G, melt
viscosity of 110 Pas at 400.degree. C.) is added into a three-neck
flask containing 120 ml of concentrated sulfuric acid (98%) at room
temperature under stirring electrically. The three-neck flask is
then put into a thermostatic waterbath at a set temperature of
30.degree. C. and allowed to react for 3.5 hours. Then the
temperature of the thermostatic waterbath is increased to
75.degree. C. and maintained for 2 hours. After the reaction
finishes, the resulting slurry from the reaction in the three-neck
flask is poured into a screen with 2 mm mesh size made of
polypropylene. The slurry flows through the screen mesh in strip
shapes and comes into cool deionized water. Strip-like polymer
materials are formed after the slurry contacts with cool deionized
water. Then the strip-like polymer is taken out and washed with
deionized water several times to remove the free acid in the
polymer until the pH of the water after washing is about 7. The
washed strip-like polymer is placed into a drying oven and dried at
120.degree. C. for 4 hours until the strip-like polymer turns
red-brown. The dried sulfonated poly(ether-ketone) 1 is crushed for
later use. The degree of sulfonation of the sulfonated
poly(ether-ketone) 1 is measured as 105% by titration method.
[0062] 10 g of poly(ether-ketone) (Victrex PLC, 22 G, melt
viscosity of 110 Pas at 400.degree. C.) is added into a three-neck
flask containing 90 ml of concentrated sulfuric acid (98%) at room
temperature under stirring electrically. The three-neck flask is
then put into a thermostatic waterbath at a set temperature of
30.degree. C. and allowed to react for 3.5 hours. Then the
temperature of the thermostatic waterbath is increased to
65.degree. C. and maintained for 2.5 hours. After the reaction
finishes, the resulting slurry from the reaction in the three-neck
flask is poured into a screen with 2 mm mesh size made of
polypropylene. The slurry flows through the screen mesh in strip
shapes and comes into cool deionized water. Strip-like polymer
materials are formed after the slurry contacts with cool deionized
water. Then the strip-like polymer is taken out and washed with
deionized water several times to remove the free acid in the
polymer until the pH of the water after washing is about 7. The
washed strip-like polymer is placed into a drying oven and dried at
120.degree. C. for 4 hours until the strip-like polymer turns
red-brown. The dried sulfonated poly(ether-ketone) 2 is crushed for
later use. The degree of sulfonation of the sulfonated
poly(ether-ketone) 2 is measured as 85% by titration method.
2. Preparation of Sulfonated poly(ether-ether-ketone)
[0063] 10 g of poly(ether-ether-ketone) (Victrex PLC, 381 G, melt
viscosity of 381 Pas at 400.degree. C.) is added into a three-neck
flask containing 100 ml of concentrated sulfuric acid (98%) at room
temperature under stirring electrically. The three-neck flask is
then put into a thermostatic waterbath at a set temperature of
35.degree. C. and allowed to react for 3 hours. Then, the
temperature of the thermostatic waterbath is increased to
75.degree. C. and maintained for 3.5 hours. After the reaction
finishes, the resulting slurry from the reaction in the three-neck
flask is poured into a screen with 2 mm mesh size made of
polypropylene. The slurry flows through the screen mesh in strip
shapes and comes into cool deionized water. Strip-like polymer
materials are formed after the slurry contacts with cool deionized
water. Then, the strip-like polymer is taken out and washed with
deionized water several times to remove the free acid in the
polymer until the pH of the water after washing is about 7. The
washed strip-like polymer is placed into a drying oven and dried at
120.degree. C. for 4 hours until the strip-like polymer turns
red-brown. The dried sulfonated poly(ether-ether-ketone) 1 is
crushed for later use. The degree of sulfonation of the sulfonated
poly(ether-ether-ketone) 1 is measured as 98% by titration
method.
[0064] 10 g of poly(ether-ether-ketone) (Victrex PLC, 381 G, melt
viscosity of 381 Pas at 400.degree. C.) is added into a three-neck
flask containing 80 ml of concentrated sulfuric acid (98%) at room
temperature under stirring electrically. The three-neck flask is
then put into a thermostatic waterbath at a set temperature of
35.degree. C. and allowed to react for 3 hours. Then, the
temperature of the thermostatic waterbath is increased to
65.degree. C. and maintained for 3 hours. After the reaction
finished, the resulting slurry from the reaction in the three-neck
flask is poured into a screen with 2 mm mesh size made of
polypropylene. The slurry flows through the screen mesh in strip
shapes and comes into cool deionized water. Strip-like polymer
materials are formed after the slurry contacts with cool deionized
water. Then, the strip-like polymer is taken out and washed with
deionized water several times to remove the free acid in the
polymer until the pH of the water after washing is about 7. The
washed strip-like polymer is placed into a drying oven and dried at
120.degree. C. for 4 hours until the strip-like polymer turns
red-brown. The dried sulfonated poly(ether-ether-ketone) 2 is
crushed for later use. The degree of sulfonation of the sulfonated
poly(ether-ketone) 2 is measured as 68% by titration method.
[0065] The polymer blend proton exchange membrane in Examples 1 to
10 and comparative Examples 1 to 4 are manufactured by using the
sulfonated polymer with various degrees of sulfonation prepared
according to the above described preparation examples of sulfonated
polymer respectively.
Example 1
[0066] 0.10 g of PVDF powder is put into a vial containing 7.8 ml
of N,N-dimethylformamide and stirred magnetically at room
temperature for 30 min to form a uniform solution. The solution is
filtered to remove any possible small particles. 0.90 g of
sulfonated poly(ether-ketone) 1 (degree of sulfonation: 105%)
prepared according to the above described preparation example 1 of
sulfonated polymer is weighed and added into the solution. The vial
is placed into a drying oven at 60.degree. C. to dissolve the
sulfonated poly(ether-ketone) thoroughly before the vial is taken
out from the drying oven. A uniform membrane forming solution of 12
wt % is obtained after stirring repeatedly. The membrane forming
solution is poured onto a glass plate to conduct tape casting, then
dried at 60.degree. C. for 12 hours and heat-treated at 100.degree.
C. for 4 hours, then naturally cooled to room temperature. Then,
the glass plate together with the membrane thereon is placed into
deionized water. The membrane is peeled off and immersed in 1 M of
sulfuric acid for a whole day. Then, the membrane is washed with
deionized water repeatedly and immersed in deionized water for
later use. The dry thickness of the resulting membrane is 85 .mu.m,
the content of PVDF is 10 wt %.
Example 2
[0067] 0.15 g of PS is put into a vial containing 7.8 ml of
N,N-dimethylformamide and stirred magnetically at room temperature
for 30 min to form a uniform solution. The solution is filtered to
remove any possible small particles. 0.85 g of sulfonated
poly(ether-ketone) 1 (degree of sulfonation: 105%) prepared
according to the above described preparation example 1 of
sulfonated polymer is weighed and added into the solution. The vial
is placed into a drying oven at 60.degree. C. to dissolve the
sulfonated poly(ether-ketone) thoroughly before the vial is taken
out from the drying oven. Then, a uniform membrane forming solution
of 12 wt % is obtained after stirring repeatedly and dispersing
with ultrasound. The membrane forming solution is poured onto a
glass plate to conduct tape casting. Then the membrane formed on
the glass plate is dried at 60.degree. C. for 12 hours and
heat-treated at 100.degree. C. for 4 hours, then naturally cooled
to room temperature. Then, the glass plate together with the
membrane thereon is placed into deionized water. The membrane is
peeled off and immersed in 1 M of sulfuric acid for a whole day.
Then, the membrane is washed with deionized water repeatedly and
immersed in deionized water for later use. The dry thickness of the
resulting membrane is 82 .mu.m, the content of PS is 15 wt %.
Example 3
[0068] 0.20 g of PES powder is put into a vial containing 7.8 ml of
N,N-dimethylformamide and stirred magnetically for 30 min to form a
uniform solution. The solution is filtered to remove any possible
small particles. 0.80 g of sulfonated poly(ether-ketone) 1 (degree
of sulfonation: 105%) prepared according to the above described
preparation example 1 of sulfonated polymer is weighed and added
into the solution. The vial is placed into a drying oven at
60.degree. C. to dissolve the sulfonated poly(ether-ketone)
thoroughly before the vial is taken out from the drying oven. Then,
a uniform membrane forming solution of 12 wt % is obtained after
stirring repeatedly and dispersing with ultrasound. The membrane
forming solution is poured onto a glass plate to conduct tape
casting. Then the membrane formed on the glass plate is dried at
60.degree. C. for 12 hours and heat-treated at 100.degree. C. for 4
hours, then naturally cooled to room temperature. Then, the glass
plate together with the membrane thereon is placed into deionized
water. The membrane is peeled off and immersed in 1 M of sulfuric
acid for a whole day. Then, the membrane is washed with deionized
water repeatedly and then immersed in deionized water for later
use. The dry thickness of the resulting membrane is 81 .mu.m, the
content of PES is 20 wt %.
Example 4
[0069] Powders of 0.10 g of PVDF and 0.15 g of PES are put into a
vial containing 7.8 ml of N,N-dimethylformamide and stirred
magnetically for 30 min to form a uniform solution. The solution is
filtered to remove any possible small particles. 0.75 g of
sulfonated poly(ether-ketone) 1 (degree of sulfonation: 105%)
prepared according to the above described preparation example 1 of
sulfonated polymer is weighed and added into the solution. The vial
is placed into a drying oven at 60.degree. C. for 2 hours to
dissolve the sulfonated poly(ether-ketone) thoroughly before the
vial is taken out from the drying oven. Then, a uniform membrane
forming solution of 12 wt % is obtained after stirring repeatedly
and dispersing with ultrasound. The membrane forming solution is
poured onto a glass plate to conduct tape casting. Then the
membrane formed on the glass plate is dried at 60.degree. C. for 12
hours and heat-treated at 100.degree. C. for 4 hours, then
naturally cooled to room temperature. Then, the glass plate
together with the membrane thereon is placed into deionized water.
The membrane is peeled off and then immersed in 1 M of sulfuric
acid for a whole day. Then, the membrane is washed with deionized
water repeatedly and then immersed in deionized water for later
use. The dry thickness of the resulting membrane is 80 .mu.m. The
content of PVDF is 10 wt % and the content of PES is 15 wt %.
Example 5
[0070] Powders of 0.05 g of PVDF, 0.15 g of PES and 0.10 g of PS
are put into a vial containing 7.8 ml of N,N-dimethylformamide and
stirred magnetically for 30 min to form a uniform solution. The
solution is filtered to remove any possible small particles. 0.70 g
of sulfonated poly(ether-ketone) 1 (degree of sulfonation: 105%)
prepared according to the above described preparation example 1 of
sulfonated polymer is weighed and added into the solution. The vial
is placed into a drying oven at 60.degree. C. for 2 hours to
dissolve the sulfonated poly(ether-ketone) thoroughly before the
vial is taken out from the drying oven. Then, a uniform membrane
forming solution of 12 wt % is obtained after stirring repeatedly
and dispersing with ultrasound. The membrane forming solution is
poured onto a glass plate to conduct tape casting. Then the
membrane formed on the glass plate is dried at 60.degree. C. for 12
hours and maintained at 100.degree. C. for 4 hours, then naturally
cooled to room temperature. Then, the glass plate together with the
membrane thereon is placed into deionized water. The membrane is
peeled off and then immersed in 1 M of sulfuric acid for a whole
day. The membrane is washed with deionized water repeatedly and
then immersed in deionized water for later use. The dry thickness
of the resulting membrane is 80 .mu.m. The content of PVDF is 5 wt
%, the content of PES is 15 wt % and the content of PS is 10 wt
%.
Example 6
[0071] 0.10 g of PVDF powder is put into a vial containing 7.8 ml
of N,N-dimethylformamide and stirred magnetically at room
temperature for 30 min to form a uniform solution. The solution is
filtered to remove any possible small particles. 0.90 g of
sulfonated poly(ether-ether-ketone) 1 (degree of sulfonation: 98%)
prepared according to the above described preparation example 2 of
sulfonated polymer is weighed and added into the solution. The vial
is placed into a drying oven at 60.degree. C. to dissolve the
sulfonated poly(ether-ether-ketone) thoroughly before the vial is
taken out from the drying oven. A uniform membrane forming solution
of 12 wt % is obtained after stirring repeatedly. The membrane
forming solution is poured onto a glass plate to conduct tape
casting, then dried at 60.degree. C. for 12 hours and heat-treated
at 100.degree. C. for 4 hours, then naturally cooled to room
temperature. Then, the glass plate together with the membrane
thereon is placed into deionized water. The membrane is peeled off
and immersed in 1 M of sulfuric acid for a whole day. Then, the
membrane is washed with deionized water repeatedly and immersed in
deionized water for later use. The dry thickness of the resulting
membrane is 85 .mu.m, the content of PVDF is 10 wt %.
Example 7
[0072] 0.15 g of PS is put into a vial containing 7.8 ml of
N,N-dimethylformamide and stirred magnetically at room temperature
for 30 min to form a uniform solution. The solution is filtered to
remove any possible small particles. 0.85 g of sulfonated
poly(ether-ether-ketone) 1 (degree of sulfonation: 98%) prepared
according to the above described preparation example 2 of
sulfonated polymer is weighed and added into the solution. The vial
is placed into a drying oven at 60.degree. C. to dissolve the
sulfonated poly(ether-ether-ketone) thoroughly before the vial is
taken out from the drying oven. Then, a uniform membrane forming
solution of 12 wt % is obtained after stirring repeatedly and
dispersing with ultrasound. The membrane forming solution is poured
onto a glass plate to conduct tape casting. Then the membrane
formed on the glass plate is dried at 60.degree. C. for 12 hours
and heat-treated at 100.degree. C. for 4 hours, then naturally
cooled to room temperature. Then, the glass plate together with the
membrane thereon is placed into deionized water. The membrane is
peeled off and immersed in 1 M of sulfuric acid for a whole day.
Then, the membrane is washed with deionized water repeatedly and
immersed in deionized water for later use. The dry thickness of the
resulting membrane is 82 .mu.m, the content of PS is 15 wt %.
Example 8
[0073] 0.20 g of PES powder is put into a vial containing 7.8 ml of
N,N-dimethylformamide and stirred magnetically for 30 min to form a
uniform solution. The solution is filtered to remove any possible
small particles. 0.80 g of sulfonated poly(ether-ether-ketone) 1
(degree of sulfonation: 98%) prepared according to the above
described preparation example 2 of sulfonated polymer is weighed
and added into the solution. The vial is placed into a drying oven
at 60.degree. C. for 2 hours to dissolve the sulfonated
poly(ether-ether-ketone) thoroughly before the vial is taken out
from the drying oven. Then, a uniform membrane forming solution of
12 wt % is obtained after stirring repeatedly and dispersing with
ultrasound. The membrane forming solution is poured onto a glass
plate to conduct tape casting. Then the membrane formed on the
glass plate is dried at 60.degree. C. for 12 hours and heat-treated
at 100.degree. C. for 4 hours, then naturally cooled to room
temperature. Then, the glass plate together with the membrane
thereon is placed into deionized water. The membrane is peeled off
and immersed in 1 M of sulfuric acid for a whole day. Then, the
membrane is washed with deionized water repeatedly and then
immersed in deionized water for later use. The dry thickness of the
resulting membrane is 83 .mu.m, the content of PES is 20 wt %.
Example 9
[0074] Powders of 0.10 g of PVDF and 0.15 g of PES are put into a
vial containing 7.8 ml of N,N-dimethylformamide and stirred
magnetically for 30 min to form a uniform solution. The solution is
filtered to remove any possible small particles. 0.75 g of
sulfonated poly(ether-ether-ketone) 1 (degree of sulfonation: 98%)
prepared according to the above described preparation example 2 of
sulfonated polymer is weighed and added into the solution. The vial
is placed into a drying oven at 60.degree. C. for 2 hours to
dissolve the sulfonated poly(ether-ketone) thoroughly before the
vial is taken out from the drying oven. Then, a uniform membrane
forming solution of 12 wt % is obtained after stirring repeatedly
and dispersing with ultrasound. The membrane forming solution is
poured onto a glass plate to conduct tape casting. Then the
membrane formed on the glass plate is dried at 60.degree. C. for 12
hours and heat-treated at 100.degree. C. for 4 hours, then
naturally cooled to room temperature. Then, the glass plate
together with the membrane thereon is placed into deionized water.
The membrane is peeled off and then immersed in 1 M of sulfuric
acid for a whole day. Then, the membrane is washed with deionized
water repeatedly and then immersed in deionized water for later
use. The dry thickness of the resulting membrane is 80 .mu.m. The
content of PVDF is 10 wt % and the content of PES is 15 wt %.
Example 10
[0075] Powders of 0.05 g of PVDF, 0.15 g of PES and 0.10 g of PS
are put into a vial containing 7.8 ml of N,N-dimethylformamide and
stirred magnetically for 30 min to form a uniform solution. The
solution is filtered to remove any possible small particles. 0.70 g
of sulfonated poly(ether-ether-ketone) 1 (degree of sulfonation:
98%) prepared according to the above described preparation example
2 of sulfonated polymer is weighed and added into the solution. The
vial is placed into a drying oven at 60.degree. C. for 2 hours to
dissolve the sulfonated poly(ether-ether-ketone) thoroughly before
the vial is taken out from the drying oven. Then, a uniform
membrane forming solution of 12 wt % is obtained after stirring
repeatedly and dispersing with ultrasound. The membrane forming
solution is poured onto a glass plate to conduct tape casting. Then
the membrane formed on the glass plate is dried at 60.degree. C.
for 12 hours and maintained at 100.degree. C. for 4 hours, then
naturally cooled to room temperature. Then, the glass plate
together with the membrane thereon is placed into deionized water.
The membrane is peeled off and then immersed in 1 M of sulfuric
acid for a whole day. The membrane is washed with deionized water
repeatedly and then immersed in deionized water for later use. The
dry thickness of the resulting membrane is 80 .mu.m. The content of
PVDF is 5 wt %, the content of PES is 15 wt % and the content of PS
is 10 wt %.
Comparative Example 1
[0076] 0.10 g of PVDF powder is put into a vial containing 7.8 ml
of N,N-dimethylformamide and stirred magnetically at room
temperature for 30 min to form a uniform solution. The solution is
filtered to remove any possible small particles. 0.90 g of
sulfonated poly(ether-ketone) 2 (degree of sulfonation: 85%)
prepared according to the above described preparation example 1 of
sulfonated polymer is weighed and added into the solution. The vial
is placed into a drying oven at 60.degree. C. to dissolve the
sulfonated poly(ether-ketone) thoroughly before the vial is taken
out from the drying oven. A uniform membrane forming solution of 12
wt % is obtained after stirring repeatedly. The membrane forming
solution is poured onto a glass plate to conduct tape casting. The
membrane formed on the glass plate is dried at 60.degree. C. for 12
hours and heat-treated at 100.degree. C. for 4 hours, then
naturally cooled to room temperature. Then, the glass plate
together with the membrane thereon is placed into deionized water.
The membrane is peeled off and immersed in 1 M of sulfuric acid for
a whole day. Then, the membrane is washed with deionized water
repeatedly and immersed in deionized water for later use. The dry
thickness of the resulting membrane is 85 .mu.m, the content of
PVDF is 10 wt %.
Comparative Example 2
[0077] Powders of 0.05 g of PVDF, 0.15 g of PES and 0.10 g of PS
are put into a vial containing 7.8 ml of N,N-dimethylformamide and
stirred magnetically for 30 min to form a uniform solution. The
solution is filtered to remove any possible small particles. 0.80 g
of sulfonated poly(ether-ketone) 2 (degree of sulfonation: 85%)
prepared according to the above described preparation example 1 of
sulfonated polymer is weighed and added into the solution. The vial
is placed into a drying oven at 60.degree. C. to dissolve the
sulfonated poly(ether-ketone) thoroughly before the vial is taken
out from the drying oven. Then, a uniform membrane forming solution
of 12 wt % is obtained after stirring repeatedly and dispersing
with ultrasound. The membrane forming solution is poured onto a
glass plate to conduct tape casting. Then the membrane formed on
the glass plate is dried at 60.degree. C. for 12 hours and
maintained at 100.degree. C. for 4 hours, then naturally cooled to
room temperature. Then, the glass plate together with the membrane
thereon is placed into deionized water. The membrane is peeled off
and then immersed in 1 M of sulfuric acid for a whole day. The
membrane is washed with deionized water repeatedly and then
immersed in deionized water for later use. The dry thickness of the
resulting membrane is 81 .mu.m. The content of PVDF is 5 wt %, the
content of PES is 15 wt % and the content of PS is 10 wt %.
Comparative Example 3
[0078] 0.10 g of PVDF powder is put into a vial containing 7.8 ml
of N,N-dimethylformamide and stirred magnetically at room
temperature for 30 min to form a uniform solution. The solution is
filtered to remove any possible small particles. 0.90 g of
sulfonated poly(ether-ether-ketone) 2 (degree of sulfonation: 68%)
prepared according to the above described preparation example 2 of
sulfonated polymer is weighed and added into the solution. The vial
is placed into a drying oven at 60.degree. C. to dissolve the
sulfonated poly(ether-ether-ketone) thoroughly before the vial is
taken out from the drying oven. A uniform membrane forming solution
of 12 wt % is obtained after stirring repeatedly. The membrane
forming solution is poured onto a glass plate to conduct tape
casting. The membrane formed on the glass plate is dried at
60.degree. C. for 12 hours and heat-treated at 100.degree. C. for 4
hours, then naturally cooled to room temperature. Then, the glass
plate together with the membrane thereon is placed into deionized
water. The membrane is peeled off and immersed in 1 M of sulfuric
acid for a whole day. Then, the membrane is washed with deionized
water repeatedly and immersed in deionized water for later use. The
dry thickness of the resulting membrane is 85 .mu.m, the content of
PVDF is 10 wt %.
Comparative Example 4
[0079] Powders of 0.05 g of PVDF, 0.15 g of PES and 0.10 g of PS
are put into a vial containing 7.8 ml of N,N-dimethylformamide and
stirred magnetically for 30 min to form a uniform solution. The
solution is filtered to remove any possible small particles. 0.80 g
of sulfonated poly(ether-ether-ketone) 2 (degree of sulfonation:
85%) prepared according to the above described preparation example
2 of sulfonated polymer is weighed and added into the solution. The
vial is placed into a drying oven at 60.degree. C. to dissolve the
sulfonated poly(ether-ether-ketone) thoroughly before the vial is
taken out from the drying oven. Then, a uniform membrane forming
solution of 12 wt % is obtained after stirring repeatedly and
dispersing with ultrasound. The membrane forming solution is poured
onto a glass plate to conduct tape casting. Then the membrane
formed on the glass plate is dried at 60.degree. C. for 12 hours
and maintained at 100.degree. C. for 4 hours, then naturally cooled
to room temperature. Then, the glass plate together with the
membrane thereon is placed into deionized water. The membrane is
peeled off and then immersed in 1 M of sulfuric acid for a whole
day. The membrane is washed with deionized water repeatedly and
then immersed in deionized water for later use. The dry thickness
of the resulting membrane is 81 .mu.m. The content of PVDF is 5 wt
%, the content of PES is 15 wt % and the content of PS is 10 wt
%.
[0080] The following property tests have been made for Nafion 115
(available commercially from DuPont Company, USA) and the polymer
blend proton exchange membranes prepared according to the Examples
1 to 10 and Comparative Examples 1 to 4.
1. Vanadium Ion Permeability Test of Proton Exchange Membrane
[0081] The vanadium ion permeability of proton exchange membrane is
conducted with a permeation cell. A proton exchange membrane is
sandwiched between two half cells of the permeation cell, wherein
one half cell contains a electrolyte solution of vanadium battery
and the other half cell contains a sulfuric acid aqueous solution
with the same concentration as that of the electrolyte solution. On
testing, the two half cells are stirred simultaneously by electric
stirrer. After a certain time, the vanadium ions in the half cell
containing the electrolyte solution will enter into the half cell
containing the sulfuric acid solution by permeating the membrane,
resulting in the change of the light absorbency of the sulfuric
acid aqueous solution. The relative content of vanadium ions in the
sulfuric acid aqueous solution side can be determined by measuring
the light absorbency of the sulfuric acid aqueous solution with
ultraviolet-visible spectrometer, thus determining the vanadium
ions permeability of various membranes. In the specification,
vanadium ions permeability is indicated by the light absorbency of
the sulfuric acid aqueous solution after 100 hours.
2. Swell Property Test of Proton Exchange Membrane
[0082] Area change rate (.DELTA.S) is used to indicate the swell
property of proton exchange membrane. At room temperature, the
surface area of wet membrane (S.sub.w) is measured after a
rectangular membrane sample is immersed in water for 12 hours. The
surface area of dry membrane (S.sub.d) is measured after the above
wet membrane is dried at 80.degree. C. for 12 hours. The area
change rate .DELTA.S is calculated based on the following
equation:
.DELTA.S=(S.sub.w-S.sub.d)/S.sub.d.times.100%
3. Mechanical Property Test of Proton Exchange Membrane
[0083] The mechanical properties of proton exchange membrane are
tested according to GB1039-79 and GB1040-79.
4. Surface Resistance Test of Proton Exchange Membrane
[0084] The surface resistance of proton exchange membrane is tested
with a battery internal resistance tester using alternating current
method. On testing, the membrane is sandwiched between the two half
cells of a permeation cell. Two graphite electrode plates are
respectively fixed on the two surfaces opposite to the surfaces on
which the membrane is sandwiched. A V.sup.3.5+ electrolyte solution
(1.7 M V.sup.3.5+, 2.6 M H.sub.2SO.sub.4) is added into the two
half cells up to a predetermined height. After the electrolyte
solution become stable, the internal resistance R.sub.2 of the
permeation cell, i.e. the internal resistance between the two
graphite electrode plates is measured with the internal resistance
tester. The internal resistance R.sub.1 of the permeation cell when
the membrane is not sandwiched between the two half cells of the
permeation cell is measured under the same conditions. The
effective test area of the membrane or the opening area of the
permeation cell is S. The surface resistance of the membrane R
(.OMEGA.cm.sup.2) is calculated according to the equation
R=(R.sub.1-R.sub.2).times.S.
[0085] The test results of proton exchange membrane are listed in
Table 1.
TABLE-US-00001 TABLE 1 Breaking Ultimate Swelling Light Absorbency
of Surface Type of Thickness Strength Enlongation Ratio .DELTA.S
sulfuric acid solution Resistance@25.quadrature. Membrane (.mu.m)
(MPa) (%) (%) side after 100 hours (.OMEGA. cm.sup.2) Nafion 115
125 31 446.04 25 0.202 0.42 Example 1 85 45 282.65 22 0.086 0.38
Example 2 82 43 202.24 17 0.073 0.45 Example 3 81 47 126.09 12
0.059 0.48 Example 4 80 38 119.50 8 0.050 0.52 Example 5 80 40
108.21 6 0.047 0.60 Example 6 85 39 232.30 23 0.077 0.39 Example 7
82 37 208.69 18 0.065 0.41 Example 8 83 38 126.48 14 0.056 0.47
Example 9 80 40 118.06 8 0.050 0.56 Example 10 80 34 107.88 5 0.043
0.62 Comparative 85 42 261.25 22 0.081 0.43 Example 1 Comparative
81 31 97.18 8 0.045 0.95 Example 2 Comparative 85 40 201.40 25
0.072 0.48 Example 3 Comparative 81 30 67.66 10 0.042 0.98 Example
4
[0086] In Table 1, it is indicated that the polymer blend proton
exchange membrane according to the present invention (Examples 1 to
10) exhibits higher mechanical strength, higher dimensional
stability and lower vanadium ion permeability, compared with Nafion
115.
[0087] Based on the Examples 1 to 10 of the present invention, the
dimensional stability is improved and vanadium ion permeability is
lowered as the amount of the soluble polymer blended is
increased.
[0088] Moreover, in contrast with the comparative examples 1 to 4
in which the degree of sulfonation of the sulfonated polymer is
beyond the scope of the present invention, higher electric
conductivity can be obtained by blending more soluble polymer in
the polymer blend proton exchange membrane prepared in Examples 1
to 10 according to the present invention. For example, the polymer
blend proton exchange membranes prepared in Examples 5 and 10 still
have high electric conductivity although the amount of the blended
soluble polymer reaches 30%. In contrast, the electric conductivity
of the membrane in comparative examples 2 and 4 decreases
dramatically, i.e. the surface resistance increases
dramatically.
[0089] Thus, according to the present invention, a polymer blend
proton exchange membrane with excellent combination of properties
can be obtained by blending a specific soluble polymer in a polymer
that is obtained by sulfonating a polymer not containing fluorine.
In particular, the polymer blend proton exchange membrane according
to the present invention has an excellent compromise among
mechanical property, dimensional stability, vanadium ion
permeability and electric conductivity.
[0090] Although the present invention has been described in
connection with the specific examples for illustrative purposes,
those skilled in the art will appreciate that various
modifications, additions and substitutions are possible after
reading the specification. The present invention is intended to
cover all of these modifications, additions and substitutions
within the scope of the accompanying claims.
* * * * *